1. Field of the Invention
The present invention generally relates to an improvement of semiconductor integrated circuits wherein an epitaxial growth layer is separated by oxide film in the lateral direction, and more particularly relates to a semiconductor integrated circuit comprising a diode and a resistor for protecting the integrated circuit from surge, in the integrated circuit itself.
2. Description of the Prior Art
In semiconductor integrated circuits, it is liable that undesirable surge is introduced in the assembling process or testing process through the outside-connection terminals, to thereby deteriorate or shortcircuit some parts of the circuit. Accordingly, protection of the elements and circuits in the integrated circuit from damage by the surge is an important problem. As a measure of the protection, such construction techniques have been used as providing diodes and resistors for protection from the surges between bonding pads and circuit parts connected thereto on the semiconductor circuit wafer. The surge protection diode to be formed on the IC wafer for such purpose serves to lead the positive surge to the positive power source line and a negative surge to the ground. The surge protection resistors serve to increase time constants.
By a cooperative function of the above-mentioned diodes and resistors, the circuit elements in the semiconductor integrated circuit is protected from surges.
The diodes and resistors for protection from the surges are hitherto provided in separate island regions for respective diodes and respective resistors.
The technical configuration and problem of the conventional surge protection of the semiconductor integrated circuits is now described more in detail. As shown in FIG. 1, a resistor R of 100-1000 .OMEGA. is connected between a pin terminal "a" and a circuit terminal "b", to attenuate positive and negative surges to protect circuit elements in the semiconductor IC. A diode Di is connected between the pin terminal "a" and a power source terminal C (for V.sub.cc) of such a polarity that its cathode is connected to the power source terminal C to lead a positive surge through the power source terminal C to a power source line.
FIG. 2 is a sectional view of an essential part of a conventional semiconductor IC comprising the resistance and the diode constituting the surge protection circuit, wherein the resistor and the diode are provided individually in respectively different island regions which are separated by oxide film.
That is, on a p-conductivity type silicon substrate 1, n-conductivity type buried regions 2 and 21 are formed and thereon a p-conductivity type silicon epitaxial layer is formed and silicon oxide isolation films 4, 4, 4 are produced by converting a part of the p-conductivity type silicon epitaxial layer, to thereby make island regions 3 and 31 on the buried regions 2 and 21, respectively. On the other hand, an n-conductivity type diffused region 5 of high impurity concentration having a diffusion depth sufficient to reach to the buried region 2 is formed as a cathode region. A shallow p-conductivity type contact region 6 is produced by diffusion to serve as a part of an anode region of the diode. Further, in another island region 31, a shallow p-conductivity type diffused region 7 is formed to serve as a resistor region. Finally openings are bored at the part to form contact electrodes of the diode and the resistors, and therein an electrode 8 for connecting the anode of the diode and one terminal of the resistor. A electrode 82 contacts the other end of the resistor, and another electrode 81 to contact the cathode side of the diode. Thus, the diode part is made in the left island 3 and the resistor is made in the right island 31. In the above-mentioned configuration, since the diode and the resistor were made in different island regions 3 and 31, parts of the diode and resistor became unnecessarily large, thereby hindering high integration; and on the other hand, in the diode part the area of the p-n junction was not so large for the area of the island 3, and therefore the surge protection effect is not satisfactory.